3. Infection Flashcards
With regard to osteomyelitis, radiographs will be normal for
7-10 days
Osteomyelitis spread in children and adults
Children have hematogenous spread usually hitting the long bones (metaphysis). Adults are more likely to have direct spread (in diabetic).
General rule in osteomyelitis
Septic joints more common in adults.
Osteomyelitis more common in kids.
Classic look of osteomyelitis
Hallmarks are destruction of bone and periosteal new bone formation.
Osteomyelitis in Spine =
IV drug user
Psoas Muscle Abscess =
TB
Unilateral SI joint =
IV drug user
Osteomyelitis in Spine with Kyphosis (Gibbus Deformity) =
TB
Sequestrum
Piece of necrotic bone surround by granulation tissue
Involucrum =
Thick sheath of periosteal bone around sequestrum
Cloaca =
Defect in the periosteum (bone skin) caused by infection
Sinus Tract
A channel from the bone to the skin (lined with granulation tissue).
Chronic Osteomyelitis:
This is defined as osteomyelitis lasting longer than 6 weeks.
Draining sinus tracts are a risk factor for
squamous cell CA
Most specific sign of active chronic osteomyelitis
presence of a sequestrum (best shown with computed tomography)
MRl diagnosis of healed osteomyelitis is based on =
Return of normal fatty marrow
Acute Bacterial Osteomyelitis
3 categories
1) hematogenous seeding {most common in child)
2) contiguous spread
3) direct inoculation of the bone either from surgery or trauma.
Acute hematogenous osteomyelitis has a predilection for the long bones of the body, specifically the
MEtaphysis
which has the best blood flow and allows for spreading of the infection via small channels in the bone that lead to the subperiosteal space
In the slightly older baby (<18 months) these vessels from the metaphysis to the epiphysis atrophy and the growth plate stops the spread (although spread can still occur). This creates a “septic tank” effect. This same thing happens with certain cancers (leukemia); the garbage gets stuck in the septic tank (metaphysis). Once the growth plates fuse, this obstruction is no longer present.
Osteomyelitis
Low signal in the bone marrow on T1 imaging adjacent to an ulcer or cellulitis is diagnostic.
The Ghost Sign: Neuropathic Bone vs
Osteomyelitis in a Neuropathic Bone
A bone that becomes a ghost (poor definition of margins) on T1 imaging, but then re-appears (more morphologically distinct) on T2, or after giving IV contrast, is more likely to have osteomyelitis.
Discitis / Osteomyelitis mechanism
Infection of the disc and infection of the vertebral body nearly always go together.
The reason has to do with the route of seeding;
Typical Look of Discitis / Osteomyelitis
Epidural Abscess
This is an infected collection between the dura and periosteum.
Discitis / Osteomyelitis Trivia
Adults: Surger, procedue, systemic infection
Children: <5 = hematogeneous spread
Most common bug: Staph A - IV drug
Almost always ESR and CRP are elevated
Pediatric Discitis I Osteomyelitis
Children have direct blood supply to the intervertebral disc, so they can get isolated discitis.
Isolated Discitis is basically never seen in adults
Kid (< 4y.o.) + URTI + back pain =
Think of Pediatric discitis
Pott Disease
“spare the disc space”
have multi-level thoracic “skip ’ involvement
Buzzwords:
“Large paraspinal abscess”
“Calcified Psoas Abscess ”
“Gibbus Deformity ”
‘‘Gibbus Deformity”
TB spondylodiscitis
DDxfor Pott’s Disease
What can also have disc space preservation?
Brucellosis
“‘Tuberculosis Dactylitis” (Spina Ventosa)
Kids + Short tubular bones of the hands and fit
diaphyseal expansile lesion with soft tissue swelling.
‘‘Rice Bodies”
These are sloughed, infarcted synovium seen with end stage RA, and TB infection ofjoints
Septic Arthritis
You see this the most in large joints which have an abundant blood supply to the metaphysis (shoulder, hip, knee).
IV drug users will get it in the SIjoint, and sternoclavicularjoint.
Septic Arthritis
Loss of joint space + Destriction + osteopenia
Pneumoarthrogram Sign
If you can demonstrate air within a joint you can exclude a joint effusion.
No joint effusion = No septic joint
Necrotizing Fasciitis
Very bad = kills very quickly = rare
Hx = HIV, Transplan, DM, alcoholics
From Group A strep
GAS in soft tissues
Necrotizing Fasciitis in Scrotum =
Fournier Gangrene
